1. Field of the Invention
The invention relates to technology of a current interrupting device of a sealed battery.
2. Description of Related Art
A sealed battery is a battery configured with an electrode body that includes a positive electrode and a negative electrode being sealed, together with an electrolyte, inside a battery case. A lithium-ion secondary battery is one well-known example of a sealed battery. Some sealed batteries are provided with a current interrupting device that detects overcharge and interrupts current. One such known current interrupting device is a pressure-type current interrupting device that physically interrupts current when the internal pressure of the battery case becomes higher than a set pressure (for example, Japanese Patent Application Publication No. 2010-212034 (JP 2010-212034 A)).
A related pressure-type current interrupting device such as that described in JP 2010-212034 A includes a conductive member that is electrically connected to an external terminal of a battery case, a collector terminal that is arranged inside the battery case, and a reversing plate that is interposed between the conductive member and the collector terminal. The conductive member is formed in a recessed shape that is recessed upward, and the entire circumference of the reversing plate is joined to a bottom portion of the conductive member by welding.
Problems with a related pressure-type current interrupting device 500 will now be described with reference to FIG. 6. FIG. 6 is a view showing a frame format of the related pressure-type current interrupting device 500.
First, the structure of the pressure-type current interrupting device 500 will be described. The pressure-type current interrupting device 500 is designed to electrically cut off a rivet 540 that serves as a conductive member from a collector terminal, not shown. The pressure-type current interrupting device 500 includes the rivet 540 and a reversing plate 550.
A recessed portion 543 of the rivet 540 is formed in a recessed shape that is recessed upward. A receiving portion 544 is formed on an inside surface of a lower end portion of the recessed portion 543. The reversing plate 550 is formed in a discoid shape. The entire circumference of an edge portion of the reversing plate 550 is joined by welding to an inner peripheral surface of the receiving portion 544 of the rivet 540.
Now the operation and problems of the pressure-type current interrupting device 500 will be described. If the pressure inside the battery case becomes higher than a set pressure due to some sort of abnormality, internal pressure P is applied to the reversing plate 550, causing the reversing plate 550 to deform in such a way that it bends upward.
When the internal pressure P is applied to the reversing plate 550 causing the reversing plate 550 to deform at this time, shearing stress consequently acts on a weld B via a fulcrum of leverage S. If the shearing stress applied to the weld B is greater than a predetermined stress value, the weld B may fracture. Therefore, in a pressure-type current interrupting device of a sealed battery, there is a need to reduce the shearing stress that is applied to the reversing plate when the pressure-type current interrupting device is activated.